Method of Forming a Bottom Electrode of a Magnetoresistive Random Access Memory Cell

ABSTRACT

A method of fabricating a semiconductor device is disclosed. The method includes forming an opening with a tapered profile in a first material layer. An upper width of the opening is greater than a bottom width of opening. The method also includes forming a second material layer in the opening and forming a hard mask to cover a portion of the second material layer. The hard mask aligns to the opening and has a width smaller than the upper width of the opening. The method also includes etching the second material layer by using the hard mask as an etch mask to form an upper portion of a feature with a tapered profile.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC design and material have producedgenerations of ICs where each generation has smaller and more complexcircuits than previous generations. In IC devices, magnetoresistiverandom access memory (MRAM), resistive random-access memory (RRAM),conductive bridging RAM (CBRAM), are next emerging technologies for nextgeneration embedded memory devices. As an example, MRAM is a memorydevice including an array of MRAM cells, each of which stores a bit ofdata using resistance values, rather than electronic charge. Each MRAMcell includes a magnetic tunnel junction (“MTJ”) cell, the resistance ofwhich can be adjusted to represent logic “0” or logic “1”. The MTJincludes a stack of films. The MTJ cell is coupled between top andbottom electrodes and an electric current flowing through the MTJ cellfrom one electrode to the other may be detected to determine theresistance, and therefore the logic state. Although existing methods offabricating next generation of embedded memory devices have beengenerally adequate for their intended purposes, they have not beenentirely satisfactory in all respects. For example, improvements informing a bottom electrode are desired.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a flowchart of an example method for fabricating asemiconductor device constructed in accordance with some embodiments.

FIGS. 2, 3, 4, 5, 6, 7, 8A, 8B, 9, 10A, 10B, 11, 12 and 13 arecross-sectional views of an example semiconductor device in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIG. 1 is a flowchart of a method 100 of fabricating one or moresemiconductor devices in accordance with some embodiments. The method100 is discussed in detail below, with reference to a semiconductordevice 200, shown in FIGS. 2, 3, 4, 5, 6, 7, 8A, 8B, 9, 10A, 10B, 11, 12and 13.

Referring to FIGS. 1 and 2, the method 100 begins at step 102 byproviding a substrate 210. The substrate 210 includes silicon.Alternatively or additionally, the substrate 210 may include otherelementary semiconductor such as germanium. The substrate 210 may alsoinclude a compound semiconductor such as silicon carbide, galliumarsenic, indium arsenide, and indium phosphide. The substrate 210 mayinclude an alloy semiconductor such as silicon germanium, silicongermanium carbide, gallium arsenic phosphide, and gallium indiumphosphide. In one embodiment, the substrate 210 includes an epitaxiallayer. For example, the substrate 210 may have an epitaxial layeroverlying a bulk semiconductor. Furthermore, the substrate 210 mayinclude a semiconductor-on-insulator (SOI) structure. For example, thesubstrate 210 may include a buried oxide (BOX) layer formed by a processsuch as separation by implanted oxygen (SIMOX) or other suitabletechnique, such as wafer bonding and grinding.

The substrate 210 may also include various p-type doped regions and/orn-type doped regions, implemented by a process such as ion implantationand/or diffusion. Those doped regions include n-well, p-well, lightdoped region (LDD) and various channel doping profiles configured toform various integrated circuit (IC) devices, such as a complimentarymetal-oxide-semiconductor field-effect transistor (CMOSFET), imagingsensor, and/or light emitting diode (LED). The substrate 210 may furtherinclude other functional features such as a resistor or a capacitorformed in and on the substrate.

The substrate 210 may also include various isolation regions. Theisolation regions separate various device regions in the substrate 210.The isolation regions include different structures formed by usingdifferent processing technologies. For example, the isolation region mayinclude shallow trench isolation (STI) regions. The formation of an STImay include etching a trench in the substrate 210 and filling in thetrench with insulator materials such as silicon oxide, silicon nitride,and/or silicon oxynitride. The filled trench may have a multi-layerstructure such as a thermal oxide liner layer with silicon nitridefilling the trench. A chemical mechanical polishing (CMP) may beperformed to polish back excessive insulator materials and planarize thetop surface of the isolation features.

The substrate 210 may also include a plurality of inter-level dielectric(ILD) layers such as silicon oxide, silicon nitride, silicon oxynitride,a low-k dielectric, silicon carbide, and/or other suitable layers. TheILD may be deposited by thermal oxidation chemical vapor deposition(CVD), atomic layer deposition (ALD), physical vapor deposition (PVD),thermal oxidation, combinations thereof, or other suitable techniques.

The substrate 210 also includes a plurality of first conductive features220. The first conductive features 220 may include gate stacks formed bydielectric layers and electrode layers. The dielectric layers mayinclude an interfacial layer (IL) and a high-k (HK) dielectric layerdeposited by suitable techniques, such as chemical vapor deposition(CVD), atomic layer deposition (ALD), physical vapor deposition (PVD),thermal oxidation, combinations thereof, and/or other suitabletechniques. The IL may include oxide, HfSiO and oxynitride and the HKdielectric layer may include LaO, AlO, ZrO, TiO, Ta₂O₅, Y₂O₃, SrTiO₃(STO), BaTiO₃ (BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO, HfTaO,HfTiO, (Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄, oxynitrides (SiON), and/or othersuitable materials. The electrode layer may include a single layer oralternatively a multi-layer structure, such as various combinations of ametal layer with a work function to enhance the device performance (workfunction metal layer), liner layer, wetting layer, adhesion layer and aconductive layer of metal, metal alloy or metal silicide). The MGelectrode may include Ti, Ag, Al, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, TiN,TaN, Ru, Mo, Al, WN, Cu, W, any suitable materials and/or a combinationthereof.

The first conductive features 220 may also include source/drain (S/D)features, which include germanium (Ge), silicon (Si), gallium arsenide(GaAs), aluminum gallium arsenide (AlGaAs), silicon germanium (SiGe),gallium arsenide phosphide (GaAsP), gallium antimony (GaSb), indiumantimony (InSb), indium gallium arsenide (InGaAs), indium arsenide(InAs), or other suitable materials. The S/D features 220 may be formedby epitaxial growing processes, such as CVD deposition techniques (e.g.,vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)),molecular beam epitaxy, and/or other suitable processes.

The first conductive features 220 may also include conductive featuresintegrated with the ILD layer in the substrate 210 to form aninterconnect structure configured to couple the various p-type andn-type doped regions and the other functional features (such as gateelectrodes), resulting a functional integrated circuit. In one example,the features 220 may include a portion of the interconnect structure andthe interconnect structure includes a multi-layer interconnect (MLI)structure and an ILD layer over the substrate 210 integrated with a MLIstructure, providing an electrical routing to couple various devices inthe substrate 210 to the input/output power and signals. Theinterconnect structure includes various metal lines, contacts and viafeatures (or via plugs). The metal lines provide horizontal electricalrouting. The contacts provide vertical connection between siliconsubstrate and metal lines while via features provide vertical connectionbetween metal lines in different metal layers.

In one embodiment, a barrier 225 is formed along sidewalls of the firstconductive features 220. The barrier 225 may include titanium nitride(TiN), tantalum nitride (TaN), tungsten nitride (WN), titanium siliconnitride (TiSiN), tantalum silicon nitride (TaSiN), and/or other suitablematerials. The barrier 225 may be formed by CVD, PVD, ALD, and/or othersuitable techniques.

The substrate 210 may also include a dielectric layer 230 such that itfills in spaces between first conductive features 220. The dielectriclayer 230 may include a dielectric material layer, such as siliconoxide, silicon nitride, a dielectric material layer having a dielectricconstant (k) lower than thermal silicon oxide (therefore referred to aslow-k dielectric material layer), and/or other suitable dielectricmaterial layer. A process of forming the dielectric layer 230 mayinclude CVD, spin-on coating, and/or other suitable techniques. In thepresent embodiment, a chemical mechanical polishing (CMP) process isperformed to remove excessive dielectric layer 230 such that topsurfaces of the first conductive features 220 are exposed without beingcovered by the dielectric layer 230.

Referring to FIGS. 1 and 3, method 100 proceeds to step 104 by formingfirst etch-stop- layer ESL 310 over the first conductive features 220and the dielectric layer 230. The first ESL 310 may include siliconnitride, oxynitride, silicon carbide, titanium oxide, titanium nitride,tantalum oxide, tantalum nitride, and/or any suitable materials. Thefirst ESL 310 may be deposited by a suitable technique, such as CVD,PVD, ALD, and/or other suitable technique.

Referring to FIGS. 1 and 4, method 100 proceeds to step 106 by forming aplurality openings (or interconnection vias) 315 in the first ESL 310 toexpose a portion of the top surface of respective first conductivefeature 220. In the present embodiment, the interconnection via 315 hasa tapered (or reversed tapered) profile with a wider opening at its topopening. In other words, the interconnection via 315 has a first widthw₁ at the top opening 315T and a second width w₂ at the bottom opening315B. The first width w₁ is greater than the second width w₂. A taperedprofile of the interconnection via 315 will relax process constrains ofgap filling in a subsequent process, which will be described later.

In an embodiment, the interconnection vias 315 are formed by forming apatterned photoresist layer over the first ESL 310 using aphotolithography process including photoresist coating, soft baking,exposing, post-exposure baking (PEB), developing, and hard baking. Then,the first ESL 310 is etched through the patterned photoresist layer toform the plurality of interconnection vias 315. The patternedphotoresist layer is removed thereafter using a suitable process, suchas wet stripping or plasma ashing.

In an embodiment, a tunable etching process is performed to achieve thetapered profile. For example, the etching parameters, such as etchant oran electric bias to a dry etching, can be continuously tuned to form theinterconnection via 315 with the tapered profile. In another embodiment,a dry etching process and a wet etching process are combined to form theinterconnection via 315. For example, a dry etching is applied first anda wet etching process is applied thereafter such that theinterconnection via 315 has a tapered profile. In yet anotherembodiment, a dry etching is applied first and followed by an argonsputtering to widen top opening 315T.

A dry etching process may implement chlorine-containing gas (e.g., Cl₂,CHCl₃, CCl₄, and/or BCl₃), bromine-containing gas (e.g. HBr and/orCHBr₃), iodine-containing gas, fluorine-containing gas (e.g., CF₄, SF₆,CH₂F₂, CHF₃, and/or C₂F₆), and/or other suitable gases and/or plasmas,and/or combinations thereof. A wet etching solution may include HNO₃,NH₄OH, KOH, HF, HCl, NaOH, H₃PO₄, TMAH, and/or other suitable wetetching solutions, and/or combinations thereof.

Referring to FIGS. 1 and 5, method 100 proceeds to step 108 by forming afirst conductive layer 410 over the first ESL 310. In the presentembodiment, the first conductive layer 410 may include a bottomelectrode layer of a MRAM device. The bottom electrode layer 410 mayinclude titanium (Ti), tantalum (Ta), platinum (Pt), ruthenium (Ru),titanium nitride (TiN), tantalum nitride (TaN), and/or other suitablematerials. The first conductive layer 410 may be formed by formed byCVD, PVD, ALD, and/or other suitable techniques.

In the present embodiment, the first conductive layer 410 fully (orcompletely) fills in the interconnection via 315 and extends to abovethe first ESL 310. As has been mentioned above, with the taper profile,the first conductive layer 410 conformably fills in the interconnectionvia 315 and prevents gap-filling issues such as void formation issue.The first conductive layer 410 physically contacts the conductivefeature 220 within the interconnection via 315. In some embodiments, aCMP process is performed to polish back excessive the first conductivelayer 410 and planarize the top surface of the first conductive layer410.

Referring again to FIGS. 1 and 5, method 100 proceeds to step 110 byforming a hard mask (HM) 420 over the first conductive layer 410. The HMlayer 420 may include silicon oxide, silicon nitride, oxynitride,silicon carbide, titanium oxide, titanium nitride, tantalum oxide,tantalum nitride, and/or any suitable materials. In some embodiment, theHM 420 is different from the first conductive layer 410 to achieveetching selectivity in subsequent etches The HM layer 420 may bedeposited by a suitable technique, such as CVD, PVD, ALD, spin-oncoating, and/or other suitable technique.

Referring to FIGS. 1 and 6, method 100 proceeds to step 112 by forming afirst patterned photoresist layer 510 over the HM 420. The firstpatterned photoresist layer 510 is formed by a photolithography processincluding photoresist coating, soft baking, exposing, post-exposurebaking (PEB), developing, and hard baking. The first patternedphotoresist layer 510 defines portions 515 of the HM 420 that arecovered by first patterned photoresist layer 510 while the rest of theHM 420 is uncovered. In the present embodiment, each of the coveredportions 515 of the HM 420 aligns to the respective interconnection via315 and has a third width w₃, which is smaller than the first width w₁.In an embodiment, the third width w₃ is smaller than the second widthw₂. In another embodiment, the third width w₃ is greater than the secondwidth w₂. That is, in the present embodiment the third width w₃ issmaller than the width (i.e. first width w₁) of the top portion ofinterconnection via 315 and smaller than the width (i.e. second widthw₂) of the bottom portion of interconnection via 315.

Referring to FIGS. 1 and 7, method 100 proceeds to step 114 by etchingthe HM 420 through the first patterned photoresist layer 510 such thatportions 515 form HM mandrels 520. In the present embodiment, ananisotropic etch is performed to form the HM mandrel 520 with a verticalprofile. The anisotropic etch may include a plasma etch by implementingchlorine-containing gas (e.g., Cl₂, CHCl₃, CCl₄, and/or BCl₃),bromine-containing gas (e.g. HBr and/or CHBr₃), iodine-containing gas,fluorine-containing gas (e.g., CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆),and/or other suitable gases and/or plasmas, and/or combinations thereof.As a result, each of the HM mandrels 520 carries the third width w₃.After forming the HM mandrels 520, the first patterned photoresist layer510 is removed by wet stripping and/or plasma ashing.

Referring to FIGS. 1 and 8A, method 100 proceeds to step 116 by etchingthe first conductive layer 410 by using the HM mandrels 520 as an etchmask and the first ESL 310 as an etch-stop layer. Protected by the HMmandrels 520, portions of the first conductive layer 310 underneathrespective the HM mandrels 520 form second conductive features 610. Inthe present embodiment, each of the second conductive features 610 isformed such that it has an upper portion 610U with a tapered profile anda lower portion 610L (within the interconnection via 315) with areversed taper profile, as shown in FIGS. 8A and 8B. In other words, ashape of each of the second conductive features 610 is such that it hasa third width w₃ at its top 610T, a forth width w₄ at its middle 610Mand the second width at its bottom 610B. Among these three widths, thefourth width w₄ is the greatest. In an embodiment, the fourth width w₄is same as the first width w₁. In another embodiment, the fourth widthw₄ is smaller than the first width w₁ due to the first conductive layer410 being etched down further.

In order to form the illustrated tapper profiles, in some embodiment,the etching parameters, such as etchant or an electric bias to a dryetching, can be continuously tuned to achieve the taper profile. A dryetching process may implement chlorine-containing gas (e.g., Cl₂, CHCl₃,CCl₄, and/or BCl₃), bromine-containing gas (e.g. HBr and/or CHBr₃),fluorine-containing gas (e.g., CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆),and/or other suitable gases and/or plasmas, and/or combinations thereof.In an embodiment, the dry etching process is performed by using gases ofCl₂/CF₄/HBr and argon sputtering.

In the present embodiment, the upper portion 610U serves as a bottomelectrode and the lower portion 610L serves as an interconnection viafeature. As a result, the bottom electrode 610U and the interconnectionvia feature 610L are formed simultaneously and inherit good physicalcontact to each other (one conductive feature). They also formed withdifferent profiles/shapes.

Referring to FIGS. 1 and 9, method 100 proceeds to step 118 by forming asecond ESL 710 over the first ESL 310, including over the HM mandrel 520and the upper portion 610U of the second conductive feature 610. Thesecond ESL 710 is formed similarly in many respects to the first ESL 310discussed above association with FIG. 3, including the materialsdiscussed therein.

Referring to FIGS. 1, 10A and 10B, method 100 proceeds to step 120 byrecessing the second ESL 710 and removing the HM mandrel 420 toplanarize a top surface of the upper portion 610U of the secondconductive feature 610. In the present embodiment, a CMP is performed topolish back the second ESL 710, remove the HM mandrel 420 and achieve aflat top surface of the upper portion 610U. In an embodiment, the upperportion 610U of the second conductive feature 610 may be polished back alittle bit as well. Thus, after recessing process, the remaining upperportion 610U is referred to as 610U′. Because of its tapered profile,when the upper portion 610U is recessed, the width of its top surface(namely the third width w₃) becomes greater, referred to as the thirdwidth w₃′. In the present embodiment, the upper portion 610U′ serves asa bottom electrode of the device 200 and the third width w₃′ is designedto be smaller than the fourth width w₄. For a bottom electrode, asubstantially flat top surface, where a stack of emerging memory filmsis to formed on, is important to decreases surface roughness of thestack of emerging memory films and improve magnetic and electricalproperties of the device 200.

Referring to FIGS. 1 and 11, method 100 proceeds to step 122 by forminga stack of emerging memory films 810 over the upper portion 610U′. Thestack of emerging memory films 810 may include multiple layers. It isnoted that the stack of emerging memory films 810 is physically contactwith the bottom electrode 610U′.

As has been mentioned above, in the present embodiment, the bottomelectrode 610U′ is formed with a smaller top width, namely the thirdwidth w₃′. Therefore a contact area 811 between the bottom electrodes610U′ and the stack of emerging memory films 810 is quite small and thisis important for promoting desired characteristics and improvingmagnetic and electrical properties and reliability of the device 200.

In some embodiments, the stack of emerging memory films 810 includes aMTJ film stack, which includes a free layer disposed over the bottomelectrode 610U′, a barrier layer disposed over the free layer, a pinlayer disposed over the barrier layer and an anti-ferromagnetic layer(AFL) disposed over the pin layer.

One or more of layers of the stack of emerging memory films 810 may beformed by various methods, including PVD process, CVD process, ion beamdeposition, spin-on coating, metal-organic decomposition (MOD), ALD,and/or other methods known in the art.

Referring again to FIGS. 1 and 11, method 100 proceeds to step 124 byforming a second conductive layer 820 over the stack of emerging memoryfilms 810. In the present embodiment, the second conductive layer 820 isformed similarly in many respects to the first conductive layer 410discussed above associations with FIG. 5, including the materialsdiscussed therein. In some embodiment, prior to forming the secondconductive layer 820 a capping layer (not shown) is formed over thestack of emerging memory films 810 and then the second conductive layer820 is formed over the capping layer. The capping layer may includetitanium, hafnium, zirconium, and/or other suitable materials. Thecapping layer may be formed by PVD, CVD, ALD, and/or other suitabletechniques.

Referring again to FIGS. 1 and 11, method 100 proceeds to step 126 byforming a second patterned photoresist layer 910 over the secondconductive layer 820. The second patterned photoresist layer 910 definesthe photoresist layer covering a portion of the second conductive layer820 while leaving the rest of the conductive layer 820 uncovered. In thepresent embodiment, the covered portion of the second conductive layer820 aligns to the interconnection via 315 and has a fifth width w₅,which is greater than the first width w₁. In some embodiment, the fifthwidth w₅ defines a width of a top electrode and a width of the stack ofemerging memory films 810 underneath the top electrode to be formed. Insome embodiment, the second patterned photoresist layer 910 is formed bya photolithography process including photoresist coating, soft baking,exposing, post-exposure baking (PEB), developing, and hard baking.

Referring to FIGS. 1 and 12, method 100 proceeds to step 128 by etchingthe second conductive layer 820 and the stack of emerging memory films810 through the second patterned photoresist layer 910 to form a thirdconductive feature 920 and an emerging memory stack 930, respectively.In some embodiment, the third conductive feature 920 includes a topelectrode and the emerging memory stack 930 includes a MJT.

The etch process may include a wet etch, a dry etch, and/or acombination thereof. The dry etching process may implementfluorine-containing gas (e.g., CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆),chlorine-containing gas (e.g., Cl₂, CHCl₃, CCl₄, and/or BCl₃),bromine-containing gas (e.g., HBr and/or CHBr₃), iodine-containing gas,other suitable gases and/or plasmas, and/or combinations thereof. Theetch process may include a multiple-step etching to gain etchselectivity, flexibility and desired etch profile. As has been mentionedpreviously, the second ESL 710 servers as an etch stop layer to relaxetch process constraints and improve the etch process window. Afterforming the third conductive feature 920 and the stack 930, the secondpatterned photoresist layer 910 is removed by wet stripping and/orplasma ashing.

Referring to FIGS. 1 and 13, method 100 proceeds to step 130 by formingspacers 950 along sidewalls of the respective third conductive feature920 and the emerging memory stack 930. In the present embodiment, thespacer 950 provides protection for the top electrode 920 and theemerging memory stack 930 to reduce current leakage and/or dataretention. The spacers 950 may be formed by depositing a spacer materiallayer over the third conductive feature 920 and the second ESL 710, andfollowed by a spacer etch to etch the spacer material layeranisotropically. The spacer material layer may include silicon oxide,silicon nitride, oxynitride, silicon carbide, titanium oxide, titaniumnitride, tantalum oxide, tantalum nitride, and/or any suitablematerials. In the present embodiment, the spacer material layer includesa material which is different from the second conductive layer 820 andthe second ESL 710 to achieve etch selectivity in subsequent etches. Thespacer layer may be deposited by CVD, ALD, PVD, and/or other suitabletechniques. In one embodiment, the spacer material layer is deposited byALD to achieve conformable film coverage along the sidewalls of thethird conductive feature 920 and the emerging memory stack 930.

Additional steps can be provided before, during, and after the method100, and some of the steps described can be replaced or eliminated forother embodiments of the method.

Based on the above, the present disclosure offers methods for forming abottom electrode with a flat top surface and a tapper profile for anemerging memory device. The method employs forming a reversed tapperprofile for an interconnection via to relax gap filling constrains and atapper profile for the bottom electrode to have a small contact areabetween the bottom electrode and an emerging memory stack for deviceperformance enhancement. The method employs forming the interconnectionvia feature and the bottom electrode simultaneously to inherit goodcontact connection. The method demonstrates a feasible and well controlprocess for bottom electrode formation.

The present disclosure provides many different embodiments offabricating a semiconductor device that provide one or more improvementsover existing approaches. In one embodiment, a method for fabricating asemiconductor device includes forming an opening with a tapered profilein a first material layer. An upper width of the opening is greater thana bottom width of opening. The method also includes forming a secondmaterial layer in the opening and forming a hard mask to cover a portionof the second material layer. The hard mask aligns to the opening andhas a width smaller than the upper width of the opening. The method alsoincludes etching the second material layer by using the hard mask as anetch mask to form an upper portion of a feature with a tapered profile.

In another embodiment, a method includes providing a substrate having afirst conductive feature and forming a first etch-stop-layer (ESL)having a tapered opening. The tapered opening aligns to the firstconductive feature and a portion of the first conductive feature isexposed within the tapered opening. The method also includes forming afirst conductive layer in the tapered opening and extending to above thefirst ESL and forming a hard mask mandrel over the first conductivelayer. The hard mask mandrel aligns with the tapered opening and a widthof the hard mask mandrel is smaller than a width at the top of thetapered opening. The method also includes etching the first conductivelayer by using the hard mask mandrel as an etch mask to form a bottomelectrode with a tapered profile, forming a second ESL over the bottomelectrode including over the hard mask mandrel, forming an emergingmemory stack over the bottom electrode and forming a top electrode overthe emerging memory stack.

In yet another embodiment, a device includes a bottom electrode having atapered profile such that a width at a top portion of the bottomelectrode is smaller than a width at a bottom portion of the bottomelectrode. The device also includes an emerging memory stack disposedover the bottom electrode. A width of the emerging memory stack is widerthan the width at the top portion of the bottom electrode. The devicealso includes a top electrode disposed over the emerging memory stackand spacers disposed along sidewalls of the emerging memory stack andthe top electrode.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A method comprising: forming an opening with a tapered profile in afirst material layer disposed on a substrate, wherein an upper width ofthe opening is greater than a bottom width of opening; forming a secondmaterial layer in the opening; forming a hard mask to cover a portion ofthe second material layer, wherein the hard mask aligns to the opening,wherein a width of the hard mask is smaller than the upper width of theopening; and etching the second material layer by using the hard mask asan etch mask to form a conductive feature of the second material layerhaving a tapered profile such that an upper portion of the conductivefeature tapers from a first width to a second width that is smaller thanthe first width in a direction away from the substrate and a lowerportion of the conductive feature extends from the upper portion andtapers from the first width to a third width that is smaller than thefirst width in a direction towards the substrate.
 2. The method of claim1, wherein the forming the opening with the tapered profile in the firstmaterial layer includes: forming a patterned photoresist layer over thefirst material layer; and etching the first material layer through thepatterned photoresist layer.
 3. The method of claim 1, wherein the firstmaterial layer serves as an etch stop layer during etching the secondmaterial layer.
 4. The method of claim 1, wherein after etching thesecond material layer above the first material layer by using the hardmask as the etch mask to form the upper portion of the conductivefeature, the remaining second material layer within the opening formsthe lower portion of the conductive feature.
 5. The method of claim 1,further comprising: after etching the second material layer, forming athird material layer over the upper portion of the conductive featureand the first material layer; and recessing the third material layer andthe hard mask to provide a planarized top surface of the upper portionof the conductive feature.
 6. The method of claim 1, wherein the secondmaterial layer includes a conductive layer.
 7. The method of claim 6,wherein the upper portion of the conductive feature includes a bottomelectrode.
 8. The method of claim 7, further comprising: forming anemerging memory stack over the bottom electrode; forming a top electrodeover the emerging memory stack; and forming spacers along sidewalls ofthe emerging memory stack and the top electrode.
 9. The method of claim8, wherein the forming the emerging memory stack over the bottomelectrode includes: forming a stack of emerging memory films over thebottom electrode; and patterning the stack of emerging memory films. 10.The method of claim 9, wherein the forming the top electrode over theemerging memory stack includes: forming a second conductive layer overthe stack of emerging memory films; forming a patterned photoresistlayer over the second conductive layer ; and etching the secondconductive layer and the stack of the emerging memory films through apatterned photoresist.
 11. A method comprising: providing a substratehaving a first conductive feature; forming a first etch-stop-layer (ESL)having a tapered opening, wherein the tapered opening aligns to thefirst conductive feature, wherein a portion of the first conductivefeature is exposed within the tapered opening; forming a firstconductive layer in the tapered opening and extending to above the firstESL; forming a hard mask mandrel over the first conductive layer,wherein the hard mask mandrel aligns with the tapered opening, wherein awidth of the hard mask mandrel is smaller than a width at the top of thetapered opening; etching the first conductive layer by using the hardmask mandrel as an etch mask to form a bottom electrode with a taperedprofile; forming a second ESL over the first ESL; forming an emergingmemory stack over the bottom electrode and the second ESL; and forming atop electrode over the emerging memory stack.
 12. The method of claim11, wherein the forming the first ESL having the tapered openingincludes: forming a patterned photoresist layer over the first ESL; andetching the first ESL, through the patterned photoresist layer.
 13. Themethod of claim 11, wherein the first ESL serves as an etch stop layerduring the etching of the first conductive layer.
 14. The method ofclaim 11, further comprising: after forming the second ESL over thefirst ESL, performing a chemical mechanical polishing (CMP) to remove aportion of the second ESL, the hard mask mandrel and a portion of thebottom electrode to expose the bottom electrode.
 15. The method of claim11, wherein the forming the emerging memory stack over the bottomelectrode includes: forming a stack of films over the bottom electrode;and patterning the stack of films.
 16. The method of claim 15, whereinthe forming the top electrode over the emerging memory stack includes:forming a second conductive layer over the stack of films; forming apatterned photoresist layer over the second conductive layer ; andetching the second conductive layer and the stack of films through thepatterned photoresist.
 17. The method of claim 11, further comprisingforming sidewall spacers along sidewalls of the emerging memory stackand the top electrode. 18-20. (canceled)
 21. A method comprising:forming an opening with a tapered profile in a first material layer,wherein an upper width of the opening is greater than a lower width ofopening; forming a second material layer in the opening; forming a hardmask to cover a first portion of the second material layer in theopening, wherein a second portion of the second material layer in theopening is not covered by the hard mask; etching the second materiallayer in the opening by using the hard mask as an etch mask to define afeature of the second material layer; forming a third material layerover an upper portion of the feature and the first material layer; andrecessing the third material layer and the hard mask to provide aplanarized top surface of the upper portion of the feature.
 22. Themethod of claim 21, wherein the forming the opening with the taperedprofile in the first material layer includes: forming a patternedphotoresist layer over the first material layer; and etching the firstmaterial layer through the patterned photoresist layer.
 23. The methodof claim 21, wherein the second material layer includes a conductivelayer.